Tanzania requires a yellow fever certificate only if you are arriving from, or have transited for more than twelve hours through, a country with yellow fever risk — which includes Kenya, Uganda, Ethiopia and much of West Africa. A direct arrival from Europe or North America does not need one. Check your exact routing, because a long layover in Nairobi or Addis can trigger the requirement.
Malaria is present across the country, at lower risk on the Ngorongoro rim and higher on the coast and in Zanzibar. Prophylaxis is strongly recommended — see your doctor or travel clinic six to eight weeks before departure to discuss options. Pack repellent with DEET, long sleeves and trousers for dusk, and use the mosquito nets provided.
Routinely recommended vaccinations are hepatitis A, typhoid, tetanus and, depending on your plans, hepatitis B and rabies. Drink only bottled or filtered water — every camp provides it. Every vehicle carries a first aid kit, all our guides hold current first aid certification, and we require every traveller to hold travel insurance that includes emergency medical evacuation; Flying Doctors cover can be arranged cheaply and is worth having.